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Патент USA US3088042

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April 30, 1963
3,088,027
M. B. GRAHAM
REFERENCE GAGE FOR RADIOGRAPHIC EXAMINATION OF TUBING
2 Sheets-Sheet 1
Filed Sept. 21, 1959
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April 30, 1963
3,088,027
M. B. GRAHAM
REFERENCE GAGE FOR RADIOGRAPHIC EXAMINATION OF TUBING
2 Sheets-Sheet 2
Filed Sept. 21, 1959
BY
1477KB/s675
United States Patent O ' ice
V
assaoz'z
Patented Apr. 30, 1963
2
1
portable X-ray equipment or a radioactive material as
the source of penetrating rays. One obstacle that has
3,088,027
heretofore appeared insurmountable to the application of
radiography to this problem was that mineral matter
REFERENCE GAGE FOR RADIOGRAPHIC
EXAMINATION OF TUBING
deposited on the inside walls of boiler tubes would at
tenuate the penetrating rays appreciably and since the
deposited material is nonuniform in character and thick
ness, a radiographic recording would manifest misleading
variations in density on the recording tending to show
Martin B. Graham, 214 Broadway, Wake?eld, Mass.
Filed Sept. 21, 1959, Ser. No. 841,419
3 Claims. (Cl. 250-65)
(Granted under Title 35, U.S. Code (1952), sec. 266)
The invention described herein may be manufactured
pits where there were none and no pit where a deep one
and used by or ‘for the Government of the United 10 existed. I discovered by experiment that the deposited
States of America for governmental purposes without
the payment of any royalties thereon or therefor.
material does not interfere with radiographic inspection.
Experiments were carried out as follows. Material that
had been deposited on the inside walls of boiler tubes was
This invention relates to a method of nondestructively
inspecting for internal pitting, boiler tubes or other
boiler parts.
.
15 obtained and was pulverized.
When a boiler is in operation, erosion pits develop
on the internal surfaces of the tubes and deepen in time
till they are serious. When the thickness of boiler tube
wall remaining beneath any pit or pits is so small that
Pairs of rectangular ?at
bars 11, 12 of material from which boiler tubes are
fabricated were utilized. One bar 12 of each pair was
machined to form a row of ?at-bottom holes of ‘gradu
ated depth according to a predetermined schedule and
ranging from zero to near 100 percent of the bar thick
it lacks the strength to withstand operating pressure in 20 ness. The holes of the one bar 12 were ?lled with the
side the tube, the weakened part of the tube ruptures.
pulverized material and another bar ‘11 without holes
The severity of the pitting is not readily predictable be
was attached over the face of bar ‘12 formed with the
holes with an adhesive type tape to hold the pair of bars
cause it is in part a function of the time distribution of
operating temperature and pressure, impurities in the
together. The pair of bars 11 and 12 as described above
feed water, frequency of peak loading and overloading 25 and another pair of identical bars but whose holes were
of the boiler and other widely ranging variables. It
free of any solid materialwere radiographed side-by
.has been common practice to carry out a periodic routine
side simultaneously in the direction of the holes using
boiler inspection by cutting sample or representative tube
one energy source and one recording ?lm. Correspond
sections from the boiler, sectioning them lengthwise, 30 ing hole images were compared with a densitometer.
removing the mineral matter that deposited on the inside
surface of the tube, and then measuring the depths of
the severest pits with a micrometer. This method is
There was no signi?cant difference. Succeeding experi
very expensive and time consuming and as a direct con
radiographic examination. A commercial densitometer,
ments con?rmed the ?nding that the material deposited
on the inside of boiler tubes would not interfere with
sequence the’ boiler tube sampling cut from the boiler is
small, often too small.
The degree of care that needs to be exercised in main
taining marine boilers generally exceeds that for station
ary boilers to minimize breakdowns at sea.
namely, an H and D ‘Densitometer, manufactured by
Eastman Kodak Company was used. The hole diameter
in the bars was made about 1A" to facilitate densitom
eter readings.
Ships are
routinely overhauled periodically and during each over 40
haul the boilers are inspected for evidence of latent weak
nesses and incipient failures. The conventional inspec~
tion method, namely, that described above, for determin~
-
FIG. 2 there is shown a short length of boiler tube
stock 15, not previously used in a boiler; its inner and
outer surfaces being smooth and radiographic examina
ing the severity of pitting, costs on the order of ‘ several
thousand dollars per ship, but for want of a better
method has continued in use for a long time.
An object of this invention is to provide an objec
tive non-destructive, and inexpensive method of inspecting '
tion having indicated that there are no signi?cant un
seen faults therein. A row of ?at bottom holes 16 of
graduated depths according to a predetermined schedule
are machined radially into the outer surface and in a
line parallel to the axis. The tubing 15 is used as a gage
as described below.
In carrying out a radiographic inspection of boiler tubes
the inside surfaces of boiler tubes for dangerously deep
of known material and known wall thickness in accord
pitting without removing tubes or other sections from the 50 ance’ with this invention, either a pair of bars 11 and 12
boiler.
as in FIG. 1 of the same material and thickness as the
Other objects and many of the attendant advantages
tubes to. be inspected, or a length of boiler tube as in FIG.
of this invention will be readily appreciated as the same
2 of the same material and thickness as the tubes to be
becomes better understood by reference to the follow
inspected is used as a gage. The gage 11, 12 or gage 15
ing detailed description when considered in connection 55 ‘is supported in any convenient manner with tape, bracket
with the accompanying drawings’wherein:
or other, adjacent the boiler tubing to be inspected. In
FIG. 1 shows a pair of ?at bars, face-to-face, of the
‘the boiler section shown in FIG; 3, the spacing between
same-‘material. and thickness as the boiler tubes to be
tubes is too small‘to receive atube section 15 of FIG. 2
inspected, one of the bars having a row of flat bottomed
therebetween. Therefore, the gage of FIG. 1 is used.
holes of graduated depths,
FIG. 2 shows a section of an unused boiler tube in
perspective, of the same material and wall thickness as
60 Though the gage of FIG. 2 is perhaps a more precise
standard for comparison, the gage of FIG. 1 has proved
to be satisfactory and has the advantage of being smaller
the boiler tubes to be inspected, partly broken away,
and having a row of ?at-bottomed holes of graduated
depths,
65
FIG. 3 shows the relationship between boiler tubes,
X-ray machine, and ?lm,
v
and lighter in weight. A portable X-ray machine 20 is
supported in front of the boiler tube sections and gage to
FIG. 4 shows the foil shielding on the ?lm, and
FIG. 5 shows a plot useful for accurately measuring
be radiographed. A 140 kv. “Baltospot” portable X-ray
machine manufactured by Balteau Electric Company,
Stamford, Connecticut, was used successfully. A radio
active material suitable for this purpose is radioisotope
iridium 192. The gage is oriented so that the holes
therein are generally aligned with the direction of radia
70
a pit.
tion.
Film 22 is supported on the side of the boiler tub
This invention utilizes radiography for boiler parts
inspection.
The radiography equipment may include
ing and gage opposite that facing the X-ray machine. A
3,088,027
'
3
sheet of lead foil 24 about .005 inch thick is supported
over both surfaces of the ?lm as shown in FIG. 4 to shield
the ?lm against scatter radiation. A ?exible plastic ?lm
cassette, not shown, supports the ?lm and foil, and the
combination is supported in place against the tubes with
an adhesive type of tape. The ?exible. cassette lends it
self to manipulation in the close quarters in a boiler.
4
penetrating completely through the walls of said tube
portion, and directed toward said tube portion to pene
trate the same, disposing a recording ?lm of the type
responsive to such rays exteriorly of said tube portion in
a position to intercept the rays from such source which
penetrate such tube portion, also disposing ‘adjacent to
said tube portion and between said source and said ?lm
Type AA commercial ?lm is recommended for the radio
in the path of some of said rays directly from said source
graphs. Double ?lm technique, one ?lm over the other,
maybe used so that one ?lm may be retained with the 10 and at approximately the same distance from said source
as said tube portion, a member of the same material as
boiler records or general maintenance records.
said tube portion and having in the path of such rays a
The following radiographing details are provided as a
thickness graduated in predetermined thicknesses between
guide. In radiographing “A” or ?reside tubes which have
about 100 percent and 200 percent of the thickness of the
nominal wall thickness of 0.134 inch or a total metal
thickness of 0.268 inch, a ?lm cassette 14 x 17 inches is 15 wall of said tube portion, and activating said source to
record images on said ?lm of the tube portion and mem~
attached ‘behind the tubes, the reference gage 11, 12 is
ber concurrently, whereby upon a comparison of the
taped to the cassette between two tubes located in the mid
recordings on said ?lm of said tube portion and member,
dle of the cassette, the X-ray machine described above is
of the images of any random pits in the wall of said tube
supported with a 3 foot space between the X-ray tube
and the nearest boiler tube and the exposure time is 200 20 portion and the images of the portions of different thick
nesses of said member, one can ascertain the presence of
seconds. The exposed ?lms are developed in the stand
dangerously deep pits in the wall of said tube portion.
ard manner at 68° Fahrenheit for 5 minutes using com
mercial developer.
The radiograph is inspected visually for the images of
2. A method as de?ned in claim 1 wherein said re
cording ?lm is a ?lm transparency and further including
the deepest pits which are the darkest spots. The density 25 measuring with a densitometer the densities of images
representing pits in the tube and the densities of images
of these spots are measured with a densitometer. Then,
of said graduated thicknesses.
the spots representing the holes in the gage are measured
3. A method for non-destructively inspecting the inside
with the densitometer. By comparing pit image density
surface of a portion of a boiler tube assembled in and
with hole image densities, the depth of the pits can be
forming part of a boiler, to detect dangerously deep pits
approximated fairly closely.
30 in the tube Wall, after the boiler has been in operation for
A more accurate method is to obtain the density read
a time, where the interior of the tube is inaccessible for
ing for the image of each hole in the gage, the density
direct inspection by means of inserted inspection devices,
readings for the area around each hole, for each hole
and where mineral deposits on such interior surface may
subtract from the density reading for the hole the density
?ll and cover such pits in such interior surface, which
reading for the area around that hole, then plot a curve
as in FIG. 5 with percentage wall thickness remaining
beneath the hole as abscissa and with difference in density
for each hole obtained as above, as ordinate. Then ob
35 comprises disposing a ?lm of a type responsive to rays of
the type which will penetrate the material of said tube
portion, behind and exteriorly of said tube portion but
adjacent thereto and behind a member adjacent to said
tain the density reading for the spot representing the deep
est pit and the density reading for the area surrounding 40 tube portion and having thicknesses in dilferent portions
thereof varying from about 100 percent and 200 percent
that spot, subtract from the density reading for the pit, the
of the thickness of the wall of said tube portion, and di
density reading for the area surrounding the pit, then
recting penetrating rays of said type from a source dis
from the curve obtain the percent-age wall thickness re
posed exteriorly of said tube portion and said member,
maining ‘beneath the pit.
This method is applicable to parts of a boiler other than 45 and at about the same distance from both tube portion
and member, part of said penetrating rays through said
tube portion to said ?lm and part of said penetrating rays
Obviously many modi?cations and variations of the
through said member to said ?lm, whereby upon a com
present invention are possible in the light of the above
tubing.
parison of the recordings on said ?lm of said tube portion
teachings. It is therefore to be understood that within
the scope of the appended claims the invention may be 50 and member, of the images of any random pits in the walls
of said tube portion and the images of the portions of
practiced otherwise than as speci?cally described.
different thicknesses of said member, one can ascertain
I claim:
1. A method for non-destructively inspecting the inside
surface of a portion of a boiler tube assembled in and
the presence of dangerously deep pits in the wall of said
tube portion.
forming part of a boiler, to detect dangerously deep pits 55
References Cited in the ?le of this patent
in the tube Wall, after the boiler has been in operation
UNITED STATES PATENTS
for a time, where the interior of the tube is inaccessible
for direct inspection by means of inserted inspection
2,399,650
Moyer ______________ __ May 7,
devices, and where mineral deposits on such interior sur
2,719,926
Procter ______________ .... Oct. 4,
face may ?ll and cover such pits in such interior surface, 60 " 2,812,440
Hartman _____________ __ Nov. 5,
which comprises disposing, at one side of and exterior to
2,957,987
Arnesen _____________ __ Oct. 25,
said tube portion a source of penetrating rays capable of
2,975,281
Williams _____________ __ Mar. 14,
1946
1955
1957
1960
1961
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